Localization of pyroantimonate-precipitable calcium in the endolymphatic sac of the tree frog, Hyla arborea japonica.

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Abstract
The pyroantimonate technique and a new demineralization method were employed to visualize pyroantimonate-precipitable calcium in the endolymphatic sac of the tree frog. The precipitate was determined to contain calcium (Ca) by EGTA extraction and X-ray microanalysis. The precipitate was mainly localized around calcium carbonate (CaCO3) crystals when frogs were not loaded with calcium chloride (CaCl2). When crystalline growth was accelerated by loading with CaCl2, the precipitate increased in amount, especially around the crystals and in the basement membrane (lamina rara and reticular lamina). Various degrees of precipitation were found in epithelial cells; however, neither epithelial granules nor mitochondria seemed to have a significant amount of precipitate. This study demonstrates that Ca ion accumulates around those crystals where a dense material is located. The dense material probably has an affinity for the Ca ion, and plays an important role in crystal formation. However, the transport pathway for the Ca ion into the endolymphatic lumen is still obscure.